Speaking as the recipient of a beneficial mutation, I would like to laugh here.

(for those who would like to know, my heart and lungs were significanly stronger than human norms, or than either of my parents. enough so that standard variance is unlikely. ALso I have an obvious detrimental mutation which is unlinked to this, but hey if we can screen my DNA to get rid of the downer mutation, and keep the good one...)

Where do they get this idea that all mutations are detrimental? A mutation simply means a change in the genetic structure, and it stands to reason that if this can be detrimental it can also be beneficial. The only way this couldn't be the case is if the organism was already perfectly suited to its environment, in which case as soon as this environment changed for whatever reason the possibility of a beneficial mutation would return again.